A method for preparing a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel

Abstract

The present invention discloses a method for preparing a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel, belonging to the field of membrane technology. The steps of the preparation method include: using an aqueous solution of pluronic with polyamine as the aqueous phase and an organic solution of polyacyl chloride as the oil phase, and preparing an independent polyamide layer through interfacial polymerization, and transferring it onto a substrate membrane to obtain a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel. The present invention uses pluronic hydrogel as a storage matrix for amine monomers, generates a polyamide layer on the surface of the organic solvent-gel through free interfacial polymerization, and further prepares a novel nanofiltration membrane. Compared with traditional TFC membranes, the present invention uses the viscosity of pluronic hydrogel to control the diffusion rate of piperazine, and the obtained nanofiltration membrane has a complete and thinner polyamide layer, improving the water flux of the nanofiltration membrane while maintaining a high salt rejection rate.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and particularly relates to a method for preparing a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel. Background Art

[0002] To solve the problem of the shortage of fresh water resources faced currently, many high-tech technologies have emerged, and membrane separation technology is one of them. Membrane separation technology can be used for the separation, concentration, purification, and refinement of mixed components, and has the advantages of process controllability, low cost, high efficiency, environmental protection, etc., becoming an effective way to alleviate the shortage of clean water, achieve energy conservation and emission reduction, and environmental protection. Among them, nanofiltration membranes can achieve the selective separation of monovalent / divalent salts, and have the advantages of high permeation flux and low energy consumption. They can achieve refined and resource-based treatment of water resources while having good environmental and economic benefits, and thus have been widely used. However, there are still many problems with nanofiltration membranes. For example, the "trade-off" effect between permeability and selectivity. The unsupported interfacial polymerization technology can achieve interfacial polymerization reactions without the interference of the substrate membrane. The aqueous monomers are evenly and continuously distributed, and the diffusion-reaction process between the two-phase monomers is not affected by the substrate membrane. The controllability of the film-forming reaction increases, which is beneficial to the regulation of the separation layer structure, and thus improves the separation performance of nanofiltration.

[0003] Traditional interfacial polymerization technology is greatly affected by the substrate membrane, and the existence of the pores in the substrate membrane requires a high monomer concentration to form a continuous and defect-free PA layer, and the formed PA layer is very thick, resulting in a low water flux. The "trade-off" effect between flux and salt rejection also limits the performance of nanofiltration membranes. Therefore, controlling the diffusion of monomers and synthesizing PA nanofiltration membranes with adjustable properties is still a difficult task and the direction of research efforts.

[0004] Poloxamer 407 is a triblock polymer, commonly used as a solubilizer, emulsifier, matrix, solid dispersion carrier, absorption promoter, stabilizer, etc., to increase the solubility of poorly soluble drugs, improve the stability of drugs, control the release of drugs, and improve the bioavailability of drugs, and has a wide application in the field of pharmacy. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention: Provide a method for preparing a thin-film polyamide layer nanofiltration membrane based on a thermosensitive hydrogel, comprising the following steps:

[0008] Using an aqueous solution of pluronic and polyamine as the aqueous phase and an organic solution of polyacyl chloride as the oil phase, an independent polyamide layer is prepared through interfacial polymerization and transferred onto a substrate membrane to obtain a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel;

[0009] The thickness of the thin polyamide layer does not exceed 30 nm.

[0010] Preferably, the polyamine is piperazine; the polyacyl chloride is trimesoyl chloride, isophthaloyl chloride, cyclohexane-1,3,5-tricarbonyl chloride, cyclopentane-1,3,5-tricarbonyl chloride, glyceroyl chloride or glutaryl chloride; the solvent of the organic solution of polyacyl chloride is n-hexane, n-heptane, dodecane or tetradecane.

[0011] Preferably, the preparation steps of the aqueous solution of pluronic and polyamine include: adding pluronic into water, stirring until dissolved under an ice-water bath condition, refrigerating to form a clear and transparent solution, and then adding polyamine to obtain the aqueous solution of pluronic and polyamine.

[0012] More preferably, the mass fraction of polyamine in the aqueous solution of pluronic and polyamine is 0.1-0.3%, and most preferably 0.15%.

[0013] Preferably, the mass fraction of polyacyl chloride in the organic solution of polyacyl chloride is 0.1-0.5%.

[0014] Preferably, the steps of interfacial polymerization include: first sieving the aqueous phase, pouring it into a container, heating to solidify the aqueous phase, and then adding the oil phase for interfacial polymerization.

[0015] More preferably, the heating temperature for solidifying the aqueous phase is 40 °C and the time is 3 min; the interfacial polymerization time after adding the oil phase is 60 s.

[0016] Preferably, the material of the substrate membrane is polysulfone, polyethersulfone, polyethylene, polyamide-imide, polypropylene or polyacrylonitrile.

[0017] The second technical solution of the present invention: provides a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel prepared according to the above preparation method.

[0018] The poloxamer 407 used in the present invention is an uncharged amphiphilic triblock copolymer surfactant, including a central hydrophobic PPO chain (70%) and two identical lateral hydrophilic PEO chains (30%). When the critical micelle concentration is reached, due to the dehydration of the hydrophobic PPO chain, individual copolymer molecules aggregate into spherical micelles. In the micelles, the PEO chains face the water and form hydrogen bonds. Above the critical micelle concentration and temperature, the hydrogen bonds break. As the concentration or temperature further increases, the distance between the micelles decreases and they stack into cubic aggregates, forming a semi-solid gel state. After the temperature decreases, it changes from the semi-solid gel to a liquid sol state. The hydrogel is used as a storage matrix for piperazine. Through the gel-sol transformation, the diffusion rate of piperazine molecules is slowed down. After sacrificing the hydrogel after synthesizing a thinner polyamide layer, the obtained nanofiltration membrane has a complete and thinner polyamide layer, enabling the nanofiltration membrane to have both high salt rejection and high flux.

[0019] The beneficial technical effects of the present invention are as follows:

[0020] The present invention uses a poloxamer hydrogel as a storage matrix for amine monomers, generates a polyamide layer on the surface of an organic solvent-gel through free interface polymerization, and then prepares a novel nanofiltration membrane. Compared with traditional TFC membranes, the present invention uses the viscosity of the poloxamer hydrogel to control the diffusion rate of piperazine. The obtained nanofiltration membrane has a complete and thinner polyamide layer, improving the water flux of the nanofiltration membrane while maintaining a high salt rejection rate.

[0021] The present invention uses a self-supporting interface polymerization method to avoid the influence of the porous matrix on interface polymerization.

[0022] The present invention not only improves the water flux of the nanofiltration membrane, but also maintains a high level of retention effect on divalent salt ions such as sodium sulfate. At the same time, sacrificing the hydrogel is environmentally friendly and can be applied to seawater desalination. Description of the Drawings

[0023] Figure 1 Water permeability and salt rejection rate of the thin-layer polyamide layer nanofiltration membranes prepared in Examples 1-4.

[0024] Figure 2 AFM diagrams of the thin-layer polyamide layers prepared in Examples 1-4. Among them, (a) is the thin-layer polyamide layer prepared in Example 2, (b) is the thin-layer polyamide layer prepared in Example 1, (c) is the thin-layer polyamide layer prepared in Example 3, and (d) is the thin-layer polyamide layer prepared in Example 4.

[0025] Figure 3 Retention performance of the thin-layer polyamide layer nanofiltration membrane prepared in Example 1 for four salt solutions.

[0026] Figure 4Comparison of water permeability and salt rejection rate of the thin-layer polyamide layer nanofiltration membranes prepared in Example 1 and Example 5. Detailed Description of the Invention

[0027] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0028] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention.

[0030] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0031] In the examples of the present invention, the pore size of the PES-based membrane is 0.22 μm, which is purchased from Haining Deli New Materials Technology Co., Ltd.

[0032] All raw materials used in the examples of the present invention are commercially available varieties.

[0033] Example 1

[0034] A method for preparing a thin-layer polyamide layer nanofiltration membrane based on a thermosensitive hydrogel, the steps are as follows:

[0035] (1) Preparation of poloxamer aqueous solution: Slowly add 20 g of poloxamer 407 to 100 mL of deionized water, stir at 4 °C in an ice bath for 4 h until the substance dissolves, and then place it in a 4 °C refrigerator for 24 h until completely dissolved to form a clear and transparent solution;

[0036] (2) Preparation of the aqueous solution: Add piperazine to the poloxamer aqueous solution and stir evenly to obtain an aqueous solution, and the mass fraction of piperazine in the aqueous solution is 0.15%;

[0037] (3) Preparation of the oil-phase solution: Dissolve trimesoyl chloride in n-hexane and mix it evenly by ultrasonic treatment to obtain the oil-phase solution, where the mass fraction of trimesoyl chloride in the oil-phase solution is 0.15%;

[0038] (4) Interfacial polymerization reaction: Pour the aqueous-phase solution into a water tank with a sieve, with the liquid level 0.5 cm higher than the sieve, and heat it in a 40 °C water bath for 3 min to solidify the aqueous-phase solution. Then, use a dropper to drip the oil-phase solution into the aqueous phase for 60 s. After the reaction, remove the excess oil-phase solution, transfer it to an oven at 60 °C and heat for 5 min. Take it out and let it cool. After the gel turns into a solution, slowly tilt the sieve to obtain an independent thin-layer polyamide layer, and transfer it to the PES substrate membrane to obtain a thin-layer polyamide layer nanofiltration membrane.

[0039] (5) Testing the separation performance: Place the above-prepared nanofiltration membrane in a nanofiltration device to test its separation performance. The specific process is as follows: Use a nanofiltration test device for testing. The nanofiltration test device is an independent pressure osmosis device. Among them, the effective test area of the membrane module is 15.9 cm 2 , the test stock solution is a 2000 ppm sodium sulfate solution, and the cross-flow method is adopted to control the flow rate at 44.4 cm / s and the pressure at 4 bar. Fix the nanofiltration membrane prepared in Example 1 on the membrane module. First, run the instrument for 1 h. After the operation is stable, start timing and sampling, measure the mass and conductivity of the obtained permeate, and then obtain the water permeability and salt rejection rate of the nanofiltration membrane.

[0040] Example 2

[0041] The preparation method is the same as that in Example 1, except that: in step (2), the mass fraction of piperazine in the aqueous-phase solution is 0.1%. The testing steps are the same as those in Example 1.

[0042] Example 3

[0043] The preparation method is the same as that in Example 1, except that: in step (2), the mass fraction of piperazine in the aqueous-phase solution is 0.2%. The testing steps are the same as those in Example 1.

[0044] Example 4

[0045] The preparation method is the same as that in Example 1, except that: in step (2), the mass fraction of piperazine in the aqueous-phase solution is 0.3%. The testing steps are the same as those in Example 1.

[0046] Example 5

[0047] The preparation method is the same as that in Example 1, except that the concentration of poloxamer is 0. The testing steps are the same as those in Example 1.

[0048] Application experimental example

[0049] 1. Without changing the other parameters in Example 1, adjust the concentration of piperazine to obtain nanofiltration membranes prepared from piperazine monomer solutions with four different concentrations of 0.1%, 0.15%, 0.2%, and 0.3%. Place the four prepared nanofiltration membranes in a nanofiltration device to test their separation performance. The specific process is the same as that in Example 1.

[0050] The performance of the nanofiltration membranes prepared with the above four different piperazine concentrations is as Figure 1 shown. Figure 1 It shows that as the piperazine concentration increases, the water flux gradually decreases and tends to be stable, while the salt rejection rate gradually increases and tends to be stable. This is mainly because the hydrogel affects the formation of the polyamide layer, resulting in changes in water permeation and salt rejection. Therefore, selecting an appropriate piperazine concentration can effectively improve the separation performance of the nanofiltration membrane without damaging the integrity of the polyamide layer.

[0051] 2. Without changing the other parameters in Example 1, adjust the concentration of piperazine to obtain nanofiltration membranes prepared from amine monomer solutions with four different concentrations of 0.1%, 0.15%, 0.2%, and 0.3%.

[0052] The thickness of the nanofiltration membranes prepared with the above four different piperazine concentrations is as Figure 2 shown, where (a) is the nanofiltration membrane prepared from the amine monomer solution with a concentration of 0.1% (Example 2), (b) is the nanofiltration membrane prepared from the amine monomer solution with a concentration of 0.15% (Example 1), (c) is the nanofiltration membrane prepared from the amine monomer solution with a concentration of 0.2% (Example 3), and (d) is the nanofiltration membrane prepared from the amine monomer solution with a concentration of 0.3% (Example 4). Figure 3 It shows that the thickness of the polyamide layer is uniform and all less than 30 nm, which are 28.5 ± 0.6 nm, 24.61 ± 0.3 nm, 24.90 ± 0.3 nm, and 23.51 ± 0.3 nm, respectively.

[0053] 3. Place the nanofiltration membrane prepared in Example 1 in a nanofiltration device to test its separation performance for four salts. The specific process is as follows:

[0054] Replace the test stock solution in the nanofiltration test device in Example 1 with magnesium sulfate solution, magnesium chloride solution, and sodium chloride solution with equal concentrations, respectively. The rest of the test process is the same as that in Example 1. The retention performance is as Figure 3 shown. The rejection rates for the four salt solutions are Na2SO4 > MgSO4 > NaCl > MgCl2, showing typical nanofiltration membrane retention characteristics. And the selectivity of Cl - / SO4 2- reaches 132.76, indicating that the prepared nanofiltration membrane has good selectivity for monovalent and divalent anions.

[0055] 4. Without changing the other parameters in Example 1, adjust the dosage of poloxamer 407. CIP represents conventional interfacial polymerization, indicating that the poloxamer concentration is 0 (Example 5), and GIP represents a poloxamer concentration of 20% w / v (Example 1). The testing process is the same as that in Example 1. The retention performance is as Figure 4 shown. By using poloxamer hydrogel to control the diffusion of piperazine, the obtained nanofiltration membrane has improved the water flux of the nanofiltration membrane while maintaining a high salt rejection rate compared with the traditional nanofiltration membrane. The water flux has increased from the original 5.59 L m -2 h -1 bar -1 to 14.8 L m -2 h -1 bar -1 .

[0056] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel, characterized in that: The following steps are involved: An independent polyamide layer is prepared by interfacial polymerization using a polyamine poloxamer aqueous solution as the aqueous phase and a polyacyl chloride organic solution as the oil phase, and then transferred to a base film to prepare a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel. The mass fraction of the polyamine in the poloxamer aqueous solution of the polyamine is 0.1-0.3%; The interfacial polymerization step comprises: firstly sieving the water phase, pouring it into a container, heating it to solidify the water phase, then adding the oil phase, and performing interfacial polymerization; The thickness of the thin polyamide layer does not exceed 30 nm.

2. The method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to claim 1, characterized in that: The polyamine is piperazine; the polyacid chloride is trimesoyl chloride, isophthaloyl chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanetrichloride or glutaryltrichloride; the solvent of the organic solution of the polyacid chloride is n-hexane, n-heptane, dodecane or tetradecane.

3. The method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to claim 1, characterized in that: The preparation steps of the polyamine poloxamer aqueous solution include: adding poloxamer to water, stirring in an ice-water bath until dissolved, refrigerating to form a clear and transparent solution, and then adding polyamine to obtain the polyamine poloxamer aqueous solution.

4. The method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to claim 1, characterized in that: The mass fraction of the polyacid chloride in the organic solution of the polyacid chloride is 0.1-0.5%.

5. The method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to claim 1, characterized in that: The heating temperature for solidifying the water phase was 40°C for 3 min, and the interfacial polymerization time after adding the oil phase was 60 s.

6. The method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to claim 1, characterized in that: The base film is made of polysulfone, polyethersulfone, polyethylene, polyamideimide, polypropylene or polyacrylonitrile.

7. A thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel prepared according to the method for preparing a thin polyamide layer nanofiltration membrane based on a thermosensitive hydrogel according to any one of claims 1 to 6.

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